Abstract

Development of highly concentrated formulations of protein and peptide drugs is a major challenge due to increased susceptibility to aggregation and precipitation. Numerous drug delivery systems including implantable and wearable controlled-release devices require thermally stable formulations with high concentrations due to limited device sizes and long-term use. Herein we report a highly concentrated insulin gel formulation (up to 80 mg/mL, corresponding to 2200 IU/mL), stabilized with a non-ionic amphiphilic triblock copolymer (i.e., Pluronic F-127 (PF-127)). Chemical and physical stability of insulin was found to be improved with increasing polymer concentration, as evidenced by reduced insulin fibrillation, formation of degradation products, and preserved secondary structure as measured by HPLC and circular dichroism spectroscopy, respectively. This formulation exhibits excellent insulin stability for up to 30 days in vitro under conditions of continuous shear at 37 °C, attributable to the amphiphilic properties of the copolymer and increased formulation viscosity. The mechanism of stabilizing insulin structure by PF-127 was investigated by coarse-grained molecular dynamics (CG-MD), all-atom MD, and molecular docking simulations. The computation results revealed that PF-127 could reduce fibrillation of insulin by stabilizing the secondary structure of unfolded insulin and forming hydrophobic interaction with native insulin. The gel formulations contained in microfabricated membrane-reservoir devices released insulin at a constant rate dependent on both membrane porosity and copolymer concentration. Subcutaneous implantation of the gel formulation-containing devices into diabetic rats resulted in normal blood glucose levels for the duration of drug release. These findings suggest that the thermally stable gel formulations are suitable for long-term and implantable drug delivery applications.

Notes

Acknowledgments

This work was supported partially by the Ontario Research Fund-Research Excellence (ORF-RE) Nanomaterials grant (No. RE03-058) in partnership with Sanofi Aventis and the Equipment Grants from the Natural Sciences and Engineering Research Council (NSERC) of Canada to X.Y. Wu. The NSERC CGS scholarship to J. Li and OGS Scholarship and Ben Cohen top-up awards to both J. Li and M. Chu are also acknowledged. S. Mirzaie is supported by an Islamic Azad University, Sanandaj Branch, scholarship.

Compliance with ethical standards

Animal studies

All institutional and national guidelines for the care and use of laboratory animals were followed.